It is well known in the field of microelectronics that high frequency operation, particularly switching of integrated circuits, can result in transient energy being coupled into the power supply circuit. Generally, the prevention of the coupling of undesired high frequency noise or interference into the power supply for an integrated circuit is accomplished by connecting a decoupling capacitor between the power and the ground leads of the integrated circuit. Conventional methods of decoupling include the use of decoupling capacitors external to the IC package, such as monolithic, multilayer ceramic chip capacitors. One external connection scheme of this type, which is found to be quite successful, is to mount a decoupling capacitor on the printed circuit board outside the integrated circuit. Plated-through holes in the circuit board are used to connect the capacitor to the power and ground which, in turn, makes contact with the appropriate leads of the integrated circuit. Other external connection schemes mount a decoupling capacitor either underneath the integrated circuit package or internal to the integrated circuit package. Such decoupling capacitors are commercially available from Rodgers Corporation and examples of these may be found in U.S. Pat. Nos. 4,994,936, 4,754,366 and 4,475,143.
The above decoupling techniques suffer from several deficiencies. The most serious of these resides in the fact that circuits, including the capacitors, become highly inductive at high frequencies as a consequence of the shape and length of the leads and interconnection traces between the discrete capacitor and the integrated circuit which it decouples. In high-frequency circuitry, this inductance may be sufficiently high to nullify the high-frequency effect attained by the circuit. A second deficiency is the spatial inefficiency found when employing a capacitor adjacent to an integrated circuit. The space requirements of a discrete decoupling capacitor and the required interconnection traces on a printed circuit board adversely affect the optimum component packaging density which might be achieved. Capacitors that are mounted internal to the molded integrated circuit package overcome the inductance problem but are difficult and expensive to manufacture. The steps of mounting the capacitor to the lead frame must be performed prior to encapsulation and are subject to yield issues in the manufacturing environment. Conventional methods of adding a discrete component external to the package, such as on top of or underneath the integrated circuit package, result in an inefficient package because of the cumbersome schemes utilized to connect the pins of the integrated circuit to the capacitor leads. Such methods rely upon separate metal foils or wires and are bulky and non-reproducible.
Accordingly, there continues to be a need for improved connection schemes for decoupling high-frequency noise from integrated circuits wherein the inductance within a decoupling loop is reduced to as low a level as possible.